Thyristor convertor failure detection device

Abstract

A failure detection device for a convertor which converts alternating current into a direct current through a plurality of rectifying thyristors. The waveform of the output direct current of the convertor is detected and is supplied to a band-pass filter which selectively passes the harmonic component which has a frequency corresponding to that of the AC voltage source for the convertor. The existence of the component of this frequency is characteristic of an occurrence of a failure within convertor. The amplitude of the component passing through the filter is then detected by a zener diode, and a failure signal is generated when the amplitude exceeds a predetermined level.

What is claimed is: 
     
       1. A failure detection device for a convertor circuit which converts alternating current into an output direct current through a plurality of rectifying elements connected between an alternating current voltage source and a direct current load, said failure detection device comprising: waveform detector means for detecting the waveform of said output direct current of said convertor, and for producing a waveform signal corresponding to said waveform;   harmonic component detector means connected to said waveform detector means and responsive to said waveform signal for detecting a harmonic component of said waveform, and for producing a harmonic component signal corresponding to said harmonic component, said harmonic component being a harmonic component having a frequency which is characteristic of an occurrence of a failure within said convertor; and   amplitude detector means connected to said detector means and responsive to said harmonic component signal for detecting the amplitude of said harmonic component and for producing a failure signal when said amplitude of said harmonic component exceeds a predetermined level.   
     
     
       2. A failure detection device as claimed in claim 1, wherein said harmonic component detector means comprises a band-pass filter for selectively passing the harmonic component having said frequency. 
     
     
       3. A failure detection device as claimed in claim 1 or 2, wherein said frequency of said harmonic component corresponds to the frequency of said alternating current voltage source. 
     
     
       4. A failure detection device as claimed in claim 1 or 2, wherein said waveform detector means comprises a current transformer coupled to said alternating current voltage source for detecting said alternating current flowing from said voltage source to said convertor circuit.